Today in things I didn't know in Python - sets

I'm slowly and thoroughly reading through the Python documentation. From the amount I'm learning in the process, I clearly should have done this some time ago.

Today I'm reading about sets. I knew a few things about sets:
- Sets are mutable, unordered, collections of unique objects
- You can declare an empty set with 'set()'
- You can declare a set with things in it like this: '{1, 2, 2}'
- You can get the difference, union, intersection, etc. like this:
 - my_set.thing_I_want(other_set)
- How to create a set comprehension

But there were things I didn't know about sets:
- You don't have to use the .operation() version, you can use operators! Some of which are more intuitive to me than others.

Operation	Equivalent	Result
s.issubset(t)	s <= t	test whether every element in s is in t
s.issuperset(t)	s >= t	test whether every element in t is in s
s.union(t)	s | t	new set with elements from both s and t
s.intersection(t)	s & t	new set with elements common to s and t
s.difference(t)	s - t	new set with elements in s but not in t
s.symmetric_difference(t)	s ^ t	new set with elements in either s or t but not both
s.update(t)	s |= t	return set s with elements added from t
s.intersection_update(t)	s &= t	return set s keeping only elements also found in t
s.difference_update(t)	s -= t	return set s after removing elements found in t
s.symmetric_difference_update(t)	s ^= t	return set s with elements from s or t but not both

- There is such a thing as immutable set (it's another class)*
- If you do use the operation_name function version for union, intersection, difference, or symmetric_difference, you don't need to cast the second thing to a set (it just needs to be iterable)


*Edited to add that I've realised it's depreciated and replaced by frozenset since 2.6